PGF2a
The most common clinical use of PGF2a (analogues) in mares is to induce
luteolysis, e.g. to advance or synchronize oestrus, to remove a persistent
corporus luteum or to terminate pregnancy. More recently, PGF2a has become
popular for stimulating uterine fluid evacuation, although it is not
recommended to use it after ovulation has occurred since it will compromise
luteal function and, if repeated, may comcpromise pregnancy maitenance.
The most common PGF2a products used are: natural P GF2a (10mg Lutalyse ),
cloprostenol (e.g. 250-375ug Estrumate ) or luprostiol (e.g. 7.5mg Prosolvin ).
Side effects (e.g. sweating and/or abdominal cramp) are most pronounced for
Lutalyse and least for Prosolvin . Large doses of PGF2a analogues (2-4 times
normal dose) appear to be useful in stimulating maternal behavior in mares
induced to lactate by use of dopamine antagonists such as domperiodone or
sulpiride, or in mares that are reluctant to accept their own foals.
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Prostaglandin E
Local application of prostaglandin E2 (Dinoprostone) or E1 (Misoprostol) is
claimed to promote cervical relaxation in mares. PGE2 has been used to
assist cervical dilation during (induced) parturition. PGE1 has primarily been
reported for relaxing the cervix in older maiden mares that pool uterine fluid
after breeding. Application of PGE2 to the oviducts has recently been
described as a way of treating suspected oviductal obstruction (Allen et al,
2006).
Oxytocin
The most common clinical uses of oxytocin are uterine fluid evacuation,
induction of parturition and expulsion of retained fetal membranes. For uterine
clearance, doses of 10-20 IU administered 1-4 times daily are usually preferred.
Oxytocin is the drug of choice for inducing parturition. Delivery of the fetus
usually occurs within 30-60 min and, while different administration regimes are
described, around 5 IU is sufficient when there are clear signs of ‘fetal
readiness for birth’ (i.e. mammary secretion [Ca2+] > 7.5 m/mol or 250 ppm,
[K+] > [Na+] or pH < 6.4). When parturition is induced prematurely, higher
and/or repeated doses (e.g. 20 IU) may be required.
Retention of the fetal membranes is a common, serious postpartum problem in
the mare, predisposed to by dystocia, prolonged gestation, hydrops, caesarean
section and induced parturition. Retention of the membranes beyond 3 h
postpartum is considered pathological. Complications associated with retained
fetal membranes include metritis, laminitis, septicemia and death. Oxytocin may
be given every 1-2 h starting 2-3 h after foaling. Doses of 20 IU are commonly
used, but should be reduced if the mare shows signs of colic; slow intravenous
infusion of higher doses (e.g. 40 IU over 30-60 min) has also been described.
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February
2016
East
London
Convention
Centre,
East
London,
South
Africa
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